The present invention pertains to lift-roof covers for use with load beds of light trucks, providing improved access to the load bed and extending vehicle functions to other uses. The invention relates primarily to differences from the parent application which result in providing the desired lift-roof function while 1) maintaining maximal commonality of other benefits with those provided by a conventional fixed mount load bed cover of vehicle cab height and 2) minimizing cost to the user, particularly where the user may be interested in the benefits of weather protection in a raised cover condition, or full enclosure, as for camping use, only as secondary considerations.
Various forms of fixed cover have been manufactured for use with open load bed light trucks. These prior art forms include covers fabricated primarily from molded reinforced plastic or from aluminum. In the majority of designs, these covers present a front view profile which is approximately matched with the front view profile of the passenger compartment or cab, so that maximal volume enclosure is provided relative to the vehicle frontal area and, hence, maximal load volume efficiency relative to fuel economy. The majority of these covers of the prior art are also fixedly attached to the load bed on which they are mounted, except at the rear wall area above the vehicle load bed tailgate. The rear wall usually incorporates an approximately vertical access door, or window, attached at its upper edge to the main structure of the cover by lateral hinging means and equipped with latching and locking means to provide security when closed. Such designs of fixed mount, cab height cover are hereinafter referred to as conventional fixed mount covers.
Primary objectives of load bed cover designs for light trucks include to provide secure, fully enclosed protection for a maximal load volume within capacity constraints for the vehicle and its load bed. Secondary objectives include the provision of convenient access to the cargo area and optimization of vehicle fuel economy and dynamic handling effects due to aerodynamic and weight characteristics of the cover within the constraints of other objectives. However, to some degree, when a fixed mount design is used, a conflict exists between the need for optimal fuel economy with acceptable vehicle handling and the desire for convenient access. This is because any increase in cover height above the passenger cab roof will increase the frontal area, thereby reducing fuel economy due to an associated increase in vehicle aerodynamic drag, as well as adversely affecting vehicle handling due to a raised center of gravity. Therefore, most covers incorporate a roof surface which is aerodynamically blended with that of the passenger cab. With existing conventional fixed mount designs of the prior art, although volume enclosure is near maximal relative to any vehicle fuel economy effects, access is limited to rear entry and this is via an opening which is limited, with respect to fuel economy, by the height of the vehicle passenger cab. This access may be improved with use of a sloping rear door or window and by raising the roof height toward the rear of the cover. However, such designs may compromise fuel economy and/or load volume capacity for a small improvement in access from the rear, with little or no improvement in access from the sides.
Various other types of cover have been marketed which have been designed to provide improved levels of convenience in access to the load bed, while also providing secure load enclosure when required. These include rigid covers pivoted as a single piece about a lateral axis in proximity to the upper edge of the load bed forward wall. With covers of this concept, a low profile above the load bed has been found to be necessary to maintain an acceptable appearance with a shape which avoids interference of the cover with the passenger cab, when in an open position. U.S. Pat. Nos. 3,785,698 (Dean et al), 3,923,334 (Key), 4,079,989 (Robertson) and 4,324,429 (Wilson et al) disclose load bed covers of this general concept. However, whereas such covers fail to provide full cab height over the load floor, U.S. Pat. Nos. 3,512,828 (Craft) and 4,613,181 (Rafi-Zadeh) disclose rigid covers which may be raised from a low profile, closed position to a position providing standing height over the full length of the load bed, with access from either side or from the rear. Nevertheless, in the closed position, as with any low profile cover, a large portion of the load volume is lost relative to a conventional fixed mount cover of cab height.
U.S. Pat. No. 4,221,423 (Stone) discloses a load bed cover of full cab height in which improved access is gained by a roof made up of a plurality of rigid panels hingedly attached one to another, so that a major portion of the roof may be folded clear of the load bed. However, the complexity and cost of manufacture appear prohibitive relative to a fixed roof cover.
U.S. Pat. No. 4,335,916 (Gutgsell) discloses a cover of full cab height, having a rigid lift-roof which is hinged about a lateral axis disposed along the upper horizontal surface of the cover. In an embodiment which is hinged close to the vehicle cab, increased access is afforded to the enclosed space, as by standing on the truck bed. However, this concept appears suitable only for structural fabrication in reinforced plastic, resulting in high weight with high manufacturing complexity and cost.
U.S. Pat. Nos. 4,252,363 (Rodrigue) and 4,639,034 (Amos) disclose load bed covers of full cab height in which flexible weatherproof fabric is stretched over movable rigid support hoops. The hoops and fabric expand or contract in accordion-like manner back and forth along the load bed while secured by sliding retention means at the vehicle load bed left and right walls. However, these concepts have obvious limitations in the levels of security provided, and/or high complexity in methods of manufacture and installation relative to conventional fixed mount covers. Similar access convenience may be provided with improved security by a two-section, rigid wall cover of cab height, in which a rear section may slide forward under a fixed forward section, as described in the March 1984 issue of Popular Science magazine. Again, however, manufacturing cost would appear to be high.
U.S. Pat. No. 4,101,162 (Koehn) discloses a vertically swingable camper shell which is supported by a specially constructed curved track and roller system defining opening motion of the shell with electric winch actuation. This concept appears to facilitate adaptation of a low conventional load bed cover to a lift-roof function, but severely offsets the associated cost advantage with complexity in the opening mechanism.
U.S. Pat. No. 4,756,571 (Lake), which is the parent application for the invention disclosed in this continuation-in-part application, describes a lift-roof cover in which flexible weatherproof panelling is interposed between a cover forward wall and a lift-roof structure in such a way that the lift-roof structure may be pivotally attached to the forward wall about a lateral axis in proximity to its lower edge. This structure accommodates opening of the cover for improved access by raising the lift-roof structure at the rear, and maintains weather protection between the forward wall and the lift-roof structure above the lower edge of the forward wall when in an open condition, due to the full jointing provided by the interposed flexible weatherproof panelling. This structure further facilitates adaptation to full weatherproof enclosure with the lift-roof structure in a raised position for such purposes as camping. However, where the user is concerned more with improved access convenience and less with camping use or optimal weather protection at the forward wall to lift-roof structure joint when in an open condition, said interposed flexible weatherproof panelling represents an unnecessary cost if its use may be avoided. Said interposed flexible weatherproof panelling may also be considered to detract from superior levels of security and a more acceptable appearance afforded by a lift-roof cover which presents a fully non-flexible surface similar to that of a conventional fixed mount cover when in the lowered, closed condition.